1. Field of the Invention
The present invention relates to a photometric apparatus of the type employing a solid-state imaging device provided with a vertical overflow drain.
2. Related Background Art
Various types of cameras have conventionally been available such as silver-salt still cameras of the type which record still images by using silver salt film, silver-salt movie cameras of the type which record motion images by using silver salt film, electronic still cameras of the type which record still images by using imaging devices and electronic memories such as magnetic floppy discs or the like, and video cameras of the type which record motion images by using imaging devices and magnetic tapes. Any of the above noted types of cameras is provided with a photometric apparatus for optimizing the amount of exposure with respect to film or the imaging device. For example, in the case of a particular type of electronic still camera which utilizes an imaging CCD as a photometric apparatus, the CCD is driven at the timing of photometry which is executed in response to a photographic operation and, as in a video camera for recording a motion image, during the driving of the CCD, photometry is effected while a diaphragm for exposure control is being controlled in order to supplement an insufficiency in the dynamic range thereof. In other words, in accordance with such a prior art, it has been necessary that CCD driving or diaphragm control be performed not only during exposure control but at the timing of photometry. As a result, the time period during which the CCD is driven in one photographic cycle is long and power dissipation therefore increases. This results in a reduction in the time period during which the camera can operate with a battery supply alone.
A similar problem occurs even when such a photometric apparatus is used in any camera other than the electronic still camera. In addition, even a conventional photometric system which does not utilize an imaging device as a photometric apparatus encounters a problem similar to the above-described one because any conventional type of camera is substantially the same in that a large amount of electrical power is consumed for the purpose of photometry.
An exposure-amount determining system is known in which one viewfinder field is divided into a plurality of sections so that a proper amount of exposure is determined by metering the brightnesses of the individual sections, selecting and combining the outputs therefrom, and effecting predetermined processes such as weighting, arithmetic operations and the like. (This exposure-amount determining system is hereinafter referred to as "multi-pattern photometric system"). If the photoconductive surface of an imaging CCD is constructed of a plurality of photoconductive segments in order to realize the multi-pattern photometric system with the imaging CCD, a signal processing circuit is needed for outputting the photometric outputs of the individual photoconductive segments at high speed. This signal processing circuit, however, increases the complexity of the entire circuit arrangement.
FIG. 7 is a schematic view showing a CCD of the horizontal overflow drain type which has heretofore been commonly used, and shows a structure in which photometry is performed through the photo-conductive surface of the CCD, consisting of a plurality of photoconductive segments. Reference numerals 71, 72, 73 and 74 denote electrode segments serving as overflow drains, and these electrode segments are employed for photometry utilizing photosensitive pixels a, b, c and d. In the case of such a structure, it is necessary that a plurality of overflow drains be separately formed on the device surface and, in addition, the separate overflow drains must be connected with no photo-sensitive pixels being covered. Accordingly, the process of producing such a device has required critical techniques for processing extremely fine portions, thus resulting in the problem that the yield and performance of devices becomes low.